MEXICO CITY — Debate is intensifying over armed vigilante patrols that have sprung up in crime-plagued sections of rural Mexico, particularly in the state of Guerrero, where some patrols joined forces this week with a radical teachers union that has been wreaking havoc with massive protests, vandalism and violent confrontations with police.

The two groups, on the surface, would appear to have little in common. The vigilante patrols, typically made up of masked campesinos, are among dozens that have emerged in the countryside in recent months, purporting to protect their communities from the depredations of the drug cartels. The state-level teachers union, meanwhile, has taken to the streets to protest a sweeping education reform law backed by Mexican President Enrique Peña Nieto.

Their alliance was announced in a joint meeting Sunday. A leader of the vigilantes said they were joining with the teachers because it was the vigilantes' "watchword to fight against injustice."

The groups took part in their first joint demonstration this week in Chilpancingo, the capital of the southern state, which is home to the well-known resort city of Acapulco. The vigilantes apparently chose to march unarmed, and there were no reports of serious trouble.

But there is concern that an already-volatile series of political protests may take on a violent edge.

Before the alliance was announced, stick- and pipe-wielding members of the union, known as the State Coordinating Committee of Guerrero Education Workers, three times had blocked the key freeway connecting Mexico City and Acapulco, disrupting commerce during Acapulco's crucial spring break season.

Last week, some of the union protesters attacked federal police with homemade weapons as officers removed them from the road, according to police reports carried by Notimex, the state news agency. According to police, 15 officers were injured.

The vigilantes' decision to participate in political protests is an "unpleasant Molotov cocktail," Francisco Arroyo, president of Mexico's Chamber of Deputies, told reporters Tuesday. "A state that permits its citizens to arm themselves in order to achieve justice by their own hand is a failed state."

In general, the idea of aggrieved campesinos taking up arms and demanding justice resonates deeply in the national mythos, and the vigilantes have been embraced in some quarters. In January, Guerrero Gov. Angel Aguirre proposed giving salaries and uniforms to a group that patrols the city of Ayutla.

There have been problems, however. In February, a group in the Guerrero community of Las Mesas shot and injured two tourists headed to the beach who failed to stop at a vigilante roadblock. In March, federal authorities announced the arrest of 34 members of a self-defense group in the neighboring state of Michoacan, alleging they were connected to the drug cartel Jalisco Nueva Generacion.

The newspaper Reforma counted vigilante groups in 27 of Guerrero's 81 municipalities. The Peña Nieto government, which took power in December, has downplayed their presence as the administration tries to move the focus in Mexico away from the country's persistent violence and toward a package of reforms — including the controversial education reform law — that it hopes will spur a golden age of economic growth.

Peña Nieto was visiting Japan this week, hoping to drum up investment. At a news conference Tuesday, he was asked about the developments in Guerrero. He said the vigilantes' effort to take justice into their own hands was "beyond legality" and one "that my government will have to fight."

On Wednesday, protest leaders said their new group, which includes students and union members, would be called the Guerreran Popular Movement. On Thursday, hundreds of protesters again blocked the freeway to Acapulco.

Aguirre, the governor, told a reporter that he refused to be intimidated.